Glossary of Motor Terms
Number of phases
In AC motors and brushless motors, the alternating current flowing in the windings is polyphase alternating current. For this purpose, the windings are also composed of pairs of the same number of phases. For high efficiency, 3 phases as shown below are considered optimal, and a sine wave current with a phase shifted by 120 degrees (2π/3 radian) flows. There are also two-phase motors. Many single phase AC motors and brushless motors are used in low cost setups.
